1. Field of the Invention
The present invention relates to methods of a functional region for fabrication of semiconductor members, semiconductor products, semiconductor devices, and the like. Further, the present invention relates to light emitting diode (LED) arrays, LED printer heads, and LED printers fabricated by the transfer method.
2. Related Background Art
Techniques of transferring, to a silicon substrate, constituent layers of a light emitting diode formed on a GaAs substrate via a sacrificial layer are known. U.S. Pat. No. 6,913,985 discloses such technology. More specifically, constituent layers of the light emitting diode deposited on the GaAs substrate via the sacrificial layer is initially divided into plural light emitting regions by forming grooves therein. The sacrificial layer is exposed to the groove. Then, a dry film resist is attached to constituent layers of the light emitting diode, and a support member of a mesh metal wire is bonded on the dry film resist.
Thereafter, portions of the resist other than portions right under the mesh metal wire are removed. The sacrificial layer is brought into contact with an etchant through the mesh support member to etch the sacrificial layer. Thus, the GaAs substrate is separated from the composite structure. Further, after separation of the GaAs substrate, a silicon substrate is bonded on the light emitting diode with constituent layers. The light emitting diode with constituent layers is transferred to the silicon substrate.
Japanese Patent Laid-open No. 2003-174041 discloses techniques of placing a chip portion selected from plural semiconductor chips formed on a substrate onto another substrate. More specifically, a first laminated layer structure with a device layer formed on a first substrate is prepared, and a second laminated layer structure with a release layer formed on a second substrate is prepared. Then, facing the device layer and the release layer to each other, the first laminated layer structure and the second laminated layer structure are bonded. The laminated layer structure including the device layer and the release layer is divided into plural portions in a predetermined pattern. Thus, plural chips including devices are formed on the second substrate. A predetermined chip selected from the plural chips is bonded to a predetermined position on a third substrate. Thereafter, the second substrate is separated from the selected chip at the release layer, and the selected chip is thus placed on the third substrate.
Where an LED array or the like is produced by using a compound semiconductor, such as GaAs, on a GaAs substrate, an efficient use of the GaAs substrate is beneficial because the GaAs substrate is expensive compared to the silicon substrate. Further, where the size of the GaAs substrate (for example, 2, 4, 6, or 8-inch substrate) is different from the size of the silicon substrate (for example, 4, 5, 6, 8, or 12-inch substrate), a transferable region is a region of the smaller substrate when the transfer is performed collectively or all at once per a unit of substrate. Accordingly, in order to attain an efficient transfer, sizes of both substrates with the size of the smaller one are to be accorded.
Where the transfer is performed in such a manner as disclosed in U.S. Pat. No. 6,913,985, a usable GaAs semiconductor layer is only a portion corresponding to a device formed on the silicon substrate. Thus, GaAs semiconductor corresponding to a portion between devices on the silicon substrate is abandoned without being used.
The above-described situation will be described with reference to FIGS. 19A and 19B. FIGS. 19A and 19B illustrate circuit devices formed on a silicon substrate and light emitting device layers formed on a GaAs substrate, respectively. Reference numeral 11 denotes the GaAs substrate, reference numeral 12 denotes the light emitting device layers of GaAs, reference numeral 13 denotes the silicon substrate, and reference numeral 14 denotes the circuit device formed on the silicon substrate 13. The light emitting device can be acquired by transferring the light emitting device layers 12 onto the circuit device 14. The light emitting device layers 12 are placed on or close to a portion of the circuit device 14. The size of the light emitting layers 12 is about 10 mm*50 microns, for example. In contrast thereto, the size of the circuit device 14 is about 10 mm*0.3 mm, for example. Therefore, where light emitting device layers 12 are collectively transferred onto circuit devices 14, the arrangement and transferable number of the light emitting layers 12 are limited due to the arrangement of the circuit devices 14. Consequently, a usable area of the light emitting layers 12 per a unit area of the GaAs substrate 11 is liable to be small.
On the other hand, according to techniques of Japanese Patent Laid-open No. 2003-174041, a large number of chips are formed on the first substrate, and a portion of the chips is selectively transferred on the second substrate. Therefore, chips corresponding to transfer portions on a plurality of the second substrates can be formed on the first substrate. Thus, the first substrate can be efficiently used to a certain degree. According to such techniques, however, when the chip is selectively transferred, an adhesive is deposited on the chip for transfer. Therefore, there is a possibility that the following situations occur. When the chip size is small (for example, a width is less than several hundreds microns), the adhesive is likely to protrude from an intended chip. In such a case, an unintended chip is likely to be also bonded, and an unfavorable transfer can occur. As a result, the yield is likely to decrease.
Further, as the chip size decreases, the thickness of the adhesive is to be set thin so that the adhesive does not protrude from the intended chip. If a bonding process is performed under such condition, an unintended chip is likely to be brought into contact with the second substrate, and accordingly some damage may occur.